The present invention relates to a once through fan for a gas laser apparatus provided with a rotational balance adjusting mechanism, a gas laser apparatus in which the once through fan is assembled, and a method of adjusting a rotational balance of the once through fan.
In conventional, there has been known a gas laser apparatus employing a once through fan as a blower for circulating and driving a laser gas, for example, the gas laser apparatus is shown in Unexamined Japanese Patent Publication No. 2000-133860 (hereinafter, refer to a first publication). FIG. 10 shows a gas laser apparatus disclosed in the first publication, and a description will be given below of a conventional art with reference to FIG. 10.
In FIG. 10, a gas laser apparatus 1 is provided with a laser chamber 2 for sealing a laser gas corresponding to a laser medium. Discharge electrodes (not shown) for generating electric discharge so as to excite a laser gas and oscillate a laser beam are arranged in an inner portion of the laser chamber 2 in an opposing manner. Further, once through fan 114 for circulating the laser gas within the laser chamber 2 so as to feed to a portion between the discharge electrodes is placed at a predetermined position in the inner portion of the laser chamber 2.
The once through fan 114 is provided with a blade portion 133 having a plurality of blades, blade supporting plates 134 and 134 disposed on both side surfaces of the once through fan 114 and supporting the blade portion 133, and rotary shafts 135 and 135 respectively adhered to the blade supporting plates 134 and 134. The rotary shafts 135 and 135 are rotatably supported by magnetic bearings 139 and 139 and a motor 138 drives the rotary shaft 135 so as to rotate the blade portion 133, thereby circulating the laser gas.
However, in the conventional art disclosed in the first publication, there are problems mentioned below. That is, since the once through fan 114 rotates within the laser chamber at a high speed, it is necessary to adjust a rotational balance so as to prevent a vibration. When rotating the once through fan 114 having the rotational balance unadjusted at a high speed, a vibration is generated in the laser chamber 2, so that an alignment of optical parts such as a mirror (not shown) and the like is shifted, whereby there is a case that a power of the laser beam is reduced and a wavelength is shifted from a predetermined value. Further, when the vibration is great, there is a problem that a service life of magnetic bearings 139 and 139 or the like becomes short. However, the first publication does not include a description concerning an adjustment of the rotational balance of the once through fan 114.
As the rotational balance adjusting means of the once through fan 114, for example, there has been known a structure shown in Unexamined Japanese Publication No. 9-317686 (hereinafter, refer to a second publication). FIG. 11 shows a balance adjusting apparatus of the once through fan 114 disclosed in the second publication. As shown in FIG. 11, the once through fan 114 is mounted on a rotational balance adjusting apparatus called as a balancing machine 19 and is rotated on the balancing machine 19, whereby a rotational balance is judged. Further, the rotational balance of the once through fan 114 is adjusted, for example, by attaching a weight (not shown) called as a balance weight to the blade supporting plate 134 and cutting and removing a part of the blade supporting plate 134. That is, in accordance with the conventional art, the once through fan 114 is attached to the inner portion of the laser chamber 2 after the rotational balance thereof is singly adjusted on the balancing machine 19.
However, when attaching the once through fan 114 to the laser chamber 2, a supporting condition for axially supporting the rotary shaft 135 of the once through fan 114 is changed due to a difference between a rigidity of the laser chamber 2 and a rigidity of the balancing machine 19 and the like. Accordingly, there is a problem that the vibration of the once through fan 114 is increased, so that the power of the laser beam is reduced as mentioned above and the wavelength is shifted.
Further, at a time of oscillating the laser, the laser gas having a density different from that of the atmospheric air is charged within the laser chamber 2 at a pressure different from that of the atmospheric pressure. Accordingly, even when adjusting the rotational balance of the once through fan 114 in the atmospheric air, there is a case that the rotational balance of the once through fan 114 is shifted and the vibration is increased by charging the laser gas into the laser chamber 2.
Further, in the case of employing the laser beam as a processing light source, in order to improve a processing speed, there is a requirement of increasing an output of the laser beam and increasing an oscillating frequency of the laser beam for oscillating pulses. Accordingly, since a vibration between the discharge electrodes is increased by making the once through fan 114 large and increasing a rotational number of the once through fan 114, it is required to further accurately adjust the balance.
In particular, in the case of employing the laser beam as the light source for a lithography process, it is necessary to provide a wavelength control apparatus (not shown) in the gas laser apparatus 1 and accurately control the wavelength of the laser beam. Accordingly, it is necessary to prevent a fine vibration of the once through fan 114, so that it is insufficient to adjust the rotational balance in accordance with the conventional art.
The present invention is made by solving the problems in the conventional art, and an object of the present invention is to provide a once through fan for a gas laser apparatus having a small vibration, a gas laser apparatus provided with the once through fan for the laser apparatus, and a method of adjusting a rotational balance of a once through fan for a gas laser apparatus.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a once through fan for a gas laser apparatus circulating and driving a laser gas charged within a laser chamber, wherein a mounting hole for mounting a balance weight for adjusting a rotational balance of the once through fan is provided on a peripheral edge surface of a blade supporting plate for supporting a blade portion of the once through fan.
In accordance with the structure mentioned above, for example, at a time of adjusting the rotational balance after assembling the once through fan in the gas laser apparatus, it is possible to attach and detach the balance weight from a front surface of the once through fan. Accordingly, in comparison with the case of attaching and detaching the balance weight with respect to a side surface of the once through fan, it is not necessary for an operator to insert hands thereof between the side surface of the once through fan and the laser chamber so as to treat, so that the operation can be easily performed.
Further, in accordance with the present invention, there is provided a gas laser apparatus comprising:
a laser chamber for charging a laser gas; and
a once through fan for circulating and driving the laser gas within the laser chamber,
wherein a mounting hole for mounting a balance weight for adjusting a rotational balance of the once through fan is provided on a blade supporting plate for supporting a blade portion of the once through fan.
In accordance with the structure mentioned above, it is possible to easily attach and detach the balance with respect to the mounting hole so as to adjust the rotational balance of the once through fan after placing the once through fan within the laser chamber. Accordingly, in comparison with the case of singly adjusting the rotational balance of the once through fan, it is possible to more accurately adjust the rotational balance and the vibration of the once through fan can be reduced.
Further, the gas laser apparatus may be structured such that the mounting hole for attaching the balance weight is provided on a peripheral edge surface of the blade supporting plate for supporting the blade portion.
In accordance with the structure mentioned above, for example, in comparison with the case of attaching and detaching the balance weight with respect to the side surface of the once through fan, there is not required a gap for inserting a tool or the like for mounting the balance weight to the portion between side surface of the once through fan and the laser chamber. Accordingly, it is possible to move the blade supporting plate to the inner wall of the laser chamber and it is possible to make an excimer laser apparatus compact. Further, since it is accordingly possible to shorten an interval between bearings for supporting the blade supporting plate, a rigidity of the once through fan is increased and a vibration can be reduced.
Further, in accordance with the present invention, there is provided a method of adjusting a rotational balance of a once through fan for a gas laser apparatus for circulating and driving a laser gas charged within a laser chamber, wherein a rotational balance is adjusted after attaching the once through fan to an inner portion of the laser chamber.
In accordance with the method mentioned above, since it is possible to adjust the rotational balance of the once through fan in accordance with the same condition as that of oscillating the laser, it is possible to more accurately adjust the rotational balance. Accordingly, the vibration of the once through fan can be reduced and a power reduction and a wavelength shift of the laser become small.